Using Cross Domain and Multi-Channel Signal Analysis for Embedded RF Testing

Radio frequency (RF) testing is a critical component in the development and validation of embedded systems, particularly in industries such as telecommunications, aerospace, automotive, and the Internet of Things (IoT). As embedded systems become increasingly complex, traditional RF test methods often prove insufficient to capture the complex interactions of signals across multiple domains—timing, frequency, and digital.

Multi-domain signal analysis has emerged as a powerful approach to addressing these challenges, offering engineers a comprehensive view of RF performance. This blog explores the principles, benefits, and practical applications of multi-domain signal analysis in embedded RF system testing, providing valuable insights for engineers and developers seeking to optimize their test workflows.

What is Multi-Domain Signal Analysis?

Multi-domain signal analysis involves the simultaneous examination of electronic signals in embedded systems across multiple domains to gain a holistic understanding of system behavior. Key domains include:

• Time Domain: Analyzes signal amplitude and phase over time, identifying transients, jitter, and timing issues.
• Frequency Domain: Examines signals represented as amplitude/power versus frequency, identifying spectral content, harmonics, and spurious emissions.
• Digital Domain: Analyzes signals discrete in both time and amplitude that relate to logic circuits, often encoded in specific communication protocols.

By integrating these perspectives, multi-domain analysis provides a more complete picture of RF performance than single-domain approaches, allowing engineers to diagnose issues that might be missed with isolated domain analysis.

Why Multi-Domain Analysis is Necessary for Embedded RF System Testing

Embedded RF systems, such as 5G devices, radar systems, or IoT modules, operate in environments with complex signal interactions. These systems often integrate numerous RF components—transceivers, amplifiers, antennas—within limited physical and power budgets. Multi-domain analysis is essential for several reasons:

• Comprehensive Signal Characterization: Embedded RF systems often exhibit behavior that spans multiple domains. For example, spurious emissions in the frequency domain can originate from a timing issue in the time domain. Multi-domain analysis correlates these phenomena, enabling faster root cause identification.
• Standards Compliance: Modern RF systems must comply with strict standards (e.g., 3GPP for 5G, IEEE 802.11 for Wi-Fi). Multi-domain analysis ensures that signals meet specifications in the time, frequency, and modulation domains, reducing the risk of non-compliance.
• Debug Complex Issues: Issues such as phase noise, intermodulation distortion, or modulation errors often manifest differently across domains. Multi-domain tools allow engineers to trace these issues to their source, simplifying debugging.
• Test Efficiency: By providing a single view of signal behavior, multi-domain analysis reduces the need for multiple test setups, saving time and resources during development and validation.

Key Tools and Methods for Multi-Domain Signal Analysis

To implement multi-domain signal analysis in embedded RF system testing, engineers rely on advanced tools and methods. Some of the most commonly used include:

Vector signal analyzers (VSAs) are versatile instruments that capture and analyze RF signals in the time, frequency, and modulation domains. They can demodulate complex signals (e.g., QAM, OFDM) and provide detailed metrics such as error vector magnitude (EVM), phase noise, and spectral purity. Modern VSAs often include software packages that provide multi-domain visualization, making them indispensable for embedded RF system testing.

Real-time spectrum analyzers (RTSAs) excel at capturing transient and discontinuous signals in the frequency domain with high dynamic range, which is critical for debugging issues such as spurious emissions or interference. Combined with time-domain visualization and demodulation analysis capabilities, RTSAs offer a powerful platform for cross-domain testing. All Tektronix RTSAs work with SignalVu, a comprehensive signal analysis package offering multiple correlated views: spectrum, spectrogram, time overview, amplitude, phase, and more.

High-bandwidth oscilloscopes equipped with RF analysis software can perform time-domain measurements while simultaneously providing frequency and modulation information. They are particularly useful for analyzing baseband and intermediate frequency (IF) signals in embedded systems. SignalVu on Tektronix oscilloscopes brings all the advanced RF signal analysis capabilities of VSAs and spectrum analyzers to the oscilloscope without the need for separate instruments. SignalVu runs directly on the oscilloscope or via a connected PC and uses the oscilloscope's time-domain data for real-time or post-capture RF analysis, correlating RF events (such as signal dropouts or spurious components) with time-domain events (such as power failures or processor activity).

Software-defined radio (SDR) platforms provide a flexible, programmable approach to RF testing. By combining an SDR with multi-domain analysis software, engineers can capture and process signals in real time, enabling rapid prototyping and testing of embedded RF systems.

Signal processing software tools such as MATLAB, Python (with NumPy and SciPy libraries), or specialized RF analysis platforms allow engineers to post-process captured signals. These tools support advanced techniques such as fast Fourier transform (FFT) for frequency analysis, time-frequency analysis (e.g., spectrograms), and modulation quality assessment.

Practical Applications in Embedded RF System Testing

Multi-domain signal analysis is applied at various stages of embedded RF system development, from design to manufacturing. Here are some practical examples:

5G ​​and IoT Device Validation

5G and IoT devices use complex modulation schemes (e.g., 256-QAM) and operate in congested spectral environments. Multi-domain analysis ensures that these devices maintain signal integrity under various conditions. For example, engineers can use VSA to measure EVM in the modulation domain while simultaneously verifying spectral spread in the frequency domain.

Radar and Automotive Systems

In automotive radar systems, precise timing and frequency stability are critical for accurate object detection. Multi-domain analysis helps engineers verify pulse characteristics in the time domain, evaluate chirp linearity in the frequency domain, and ensure modulation accuracy.

Wireless Communication Modules

Embedded Wi-Fi or Bluetooth modules must comply with standards while operating in noisy environments. Multi-domain analysis can identify issues such as co-channel interference (frequency domain), packet synchronization errors (time domain), or modulation distortion, ensuring reliable operation.

Satellite and Aerospace Systems

Satellite communication systems require high reliability and low phase noise. Multi-domain analysis allows engineers to validate signal quality across all domains, ensuring compliance with stringent aerospace standards.

Best Practices for Implementing Cross-Domain Signal Analysis

To maximize the benefits of multi-domain signal analysis when testing embedded RF systems, consider the following best practices:

• Define clear test objectives: Identify key performance metrics (e.g., EVM, spurious-free dynamic range) and the domains relevant to your system before testing.
• Choose the Right Tools: Choose instruments and software that support cross-domain analysis and are compatible with your system's frequency range and modulation schemes. As mentioned earlier, the Tektronix 4, 5, and 6 Series MSO oscilloscopes are an excellent solution for validating embedded RF systems without the need for separate spectrum analyzers. They enable time-correlated debugging and modulation analysis directly from the oscilloscopes.
• Correlate measurements across domains: Use visualization tools to overlay time, frequency, and modulation data, making it easier to identify relationships between anomalies. Spectrum View on Tektronix 5 and 6 Series MSO oscilloscopes is a built-in, hardware-integrated real-time spectrum analysis tool that complements SignalVu, offering simultaneous time and frequency domain views and independent control over center frequency, span, and resolution bandwidth thanks to a dedicated digital downconverter on each channel.
• Automate testing workflows: Use scripts (e.g., Python, SCPI commands) to automate multi-domain measurements, improving repeatability and efficiency. SignalVu-PC includes an automation interface (COM API) and an ecosystem of structured APIs that abstract low-level SCPI commands, making automation faster, less error-prone, and more readable.

Challenges and Future Trends

Cross-domain analysis on multiple channels can be a very expensive and complex setup, requiring various pieces of expensive equipment that must be synchronized by skilled operators. Furthermore, processing datasets from multi-domain measurements requires data acquisition on an external client with significant computing resources.

However, an oscilloscope, while not offering the same dynamic range as an RTSA and possibly fewer analysis options than a dedicated RF VSA, still represents an excellent compromise. In a well-known instrument commonly used by engineers, you can get a high-level debugging alternative "in a single box." Vector analysis can be performed within the device itself, without the need to export data externally or synchronize multiple units.

Trends Shaping the Future of Multi-Domain Signal Analysis

• AI and Machine Learning: AI-based tools are being integrated into RF test equipment to automate anomaly detection and predict system behavior across multiple domains.
• Cloud Testing: Cloud platforms enable remote multi-domain analysis, allowing teams to collaborate and process data more efficiently.
• Higher Frequencies: As millimeter-wave and terahertz systems become more common, multi-domain analysis tools are evolving to support these bands.
• Integration with Digital Twins: Multi-domain analysis is increasingly being combined with digital twin simulations to virtually validate RF systems prior to physical testing.

Conclusion

Multi-domain signal analysis is transforming embedded RF system testing, providing a comprehensive, efficient, and accurate approach to characterizing complex systems. Using tools like RTSA and oscilloscopes with advanced software, engineers can diagnose problems, ensure compliance, and optimize performance across the time, frequency, and modulation domains.

As RF systems evolve, adopting multi-domain signal analysis will be critical to maintaining leadership in the rapidly evolving world of embedded technologies. Whether you're developing 5G devices, automotive radars, or IoT modules, multi-domain signal analysis is a game-changer for achieving reliable, high-performance RF designs.